C5 x7 rear parking sensors not working but computer says yes

[GiveMeABreak]

.... loss of and re-acquisition of CAN+ may have been what was needed - and as I said previously, this is what would of happened if a BSI reset had been done.

If the operability becomes sporadic again, I would try looking at your fault code log in Diagbox to see what has been recorded (for intermittent faults) and see if you have a code listed there.